1. Field of the Invention
This invention relates to a throttle valve positioner which prevents abrupt closure of the throttle valve in the carburetor in internal combustion engines for vehicles such as automobiles and controls the throttle valve opening depending on the vacuum created in the intake passage supplying the fuel-air mixture to the engine.
2. Description of the Prior Art
Various types of throttle valve positioners have been proposed hitherto for controlling the opening of the throttle valve in the carburetor in internal combustion engines. In a prior art throttle valve positioner of one type, a diaphragm chamber formed in the throttle valve positioner body is merely connected to a vacuum bleed port located to open in the vicinity of the throttle valve disposed in the intake passage of an engine. In an engine equipped with a prior art throttle valve positioner of another type, a pulse signal generated by a speed sensor associated with the speed meter is applied to a computer which generates an output voltage when the vehicle speed exceeds a predetermined setting value, thereby energizing an electromagnetic valve (a vacuum switching valve) provided for switching the vacuum in the intake passage of the engine. The electromagnetic valve thus energized establishes a path of communication between a diaphragm chamber in the throttle valve positioner body and the atmosphere thereby energizing the throttle valve positioner. On the other hand, when the vehicle speed is reduced to a value lower than the predetermined setting, no output voltage appears from the computer to restore the electromagnetic valve to the original state or deenergized state. Consequently, the vacuum in the intake passage of the engine acts upon the diaphragm in the diaphragm chamber of the throttle valve positioner body to deenergize the throttle valve positioner.
However, the prior art throttle valve positioner of the former type has been defective in that the throttle valve tends to be abruptly closed in spite of the fact that the speed of the vehicle is still high as in the case of impartation of the engine brakes to the vehicle. The prior art throttle valve positioner of the latter type has also been defective in that the use of the elements including the speed sensor, computer and electromagnetic valve results inevitably in high costs, although it can satisfactorily reliably operate for the throttle valve control.